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W. L. CARLSON AND E. C. HANSON.

IvIE/INS FOR LocAIING ORE BODIES BY AUDIO FREQUENCY CURREIIIIS.

APPLICATION vFILED MAY 7. IUIQ.

Lzl. Patented Deo. 23,19I9.

i Ult-[TED STATES Orricn wiiNnnLL it; cAn'LsoN AND EARL c. nANsoN, or wAsHiNGroN, nis'rnicror coLimBrA.

MEANS FOB LOCATINI? OBE IBODIS BY AUDIO-FREQUENCY CUQRENTS.

"Patented Dec. 23, 1919.

Appiication niet may 7, 1919. serial Np. 295,353.

To all whom it may concer/n.' l a 4Be it knownthat we, WENDELL L. CARL- soN and EARL C. HANsoN, citizens of the United States, residing at Washington, District of Columbia, have invented new and' useful Improvements in Means for Locating Ore Bodies by Audio-Frequency .Currents, of which the following is a specification.

Our invention relates to a means for determining the location and approirimate magnitude ofbodies of ore buried in the earth.

The object of this invention is to provide simple and reliable electrical means for accuratel spotting metallic ore deposits and indicating directly the extent of the ore bodies.

Another object of this invention is to provide a portable apparatus which can be trans rted without diiiculty in the mining districts and used to explore promising ore regions to determine the position and magnitude of the metallic deposits.

A further object of this invention is to establish in an apparatus of this character*- an ex loring coil connected in a balanced electrical circuit energized by a sou rce of audio frequency current which circuit will be immediately thrown out of balance when the exploring coil is brought into the vicinity of ore bodies and thus manifest the presence of the ore by actuating a suitable responsive device.

This invention is diagrammatically illustrated in the accompanying drawin.1 which forms a part of the following speci cation.

1ideferring particularly to the drawing4 which has been selected to clearly set forth the principle advanced in the present means for locating ore bodies, reference character 1 designates an audio frequency generator, for example a 1000 cycle machine, having terminals 2 and 3. rlhe portable exploring coil 15 is connected to the audio frequency generatorY on one side by conductor 4 and on the other-side through conductor 5 and a rimary winding 6 of a diiferential transormer. A Y

VA second primary winding 7 of the same dierential transformer is connected in a circuit from terminal 2 of the audio frequenc alternator through variable` calibrate resistance 8 equipped with adjustable contact 9, returning to the terminal 3 o f the alternator through conductor 4. The differential transformer has a laminated iron core 10 and secondary winding 11 which comprises the input circuit of the audio frequenc thermionic amplifiers 12 and 13.` Althoug only two stages of am lification are shown it is obvious that ad itional stages might be employed. Responsive device 14 is connected in the output circuit of the final amplifier. This device is here shown astelephone receivers but it is a parent that any electromagnetically contro led device-might be employed. .2'

' Coil 15 is adapted to be moved oirer the area which it is desired to explore to locatev hidden ore.deposits represented b dotted lines 16 as beneath the surface of t e earth.

The variable resistance 8 is calibrated in terms of ore density. rlhis is accomplished by noting the relative energy absorbed by ore bodies due to the eddy currents induced therein by the magneticv eld emanating 4from the exploring coil. A. variation in energy absorbed by the ore body is accomcomplished by a like variation of current intensity in the exploring circuit. Ylhe differential transformer is balanced for each setting by varying the resistance 8 until the currents in windings 6 and 'l `are equal. Hence the variable amount of resistance 8 required to balance the di'erential circuits for various energy absorptions is a direct calibration of ore density.

ln the practical operation of this system for locating bodies of ore the exploring coil is placed horizontally in relation to the earth. rlhe variable contact 9 is adiusted until the resistance 8 just allows sucient current to dow through the diierential winding 7 so as to balance the magnetic eld produced by a flow of current through the "dierential winding 6. With the apparatus so balanced no tone will be produced in the telephone receivers 14, due .to the fact that the potential induced in the secondary windin 11 is zero. 0n movin the exploring coil 15 over the earths sur 'ace any change in energy absorbed due to the presence of ore causes a variation in current in the exploring coil V15, which in turn unbalances the differential windings 6 and 7 due to the unequal How of current therein. Any ininute change thus produced ,induces a voltage in the secondary winding 11- whichwill be greatly amplified by the thermionic ampliers 12 and 13 producing a clear audible tone in the telephone receivers 11i. The mass ancing the reactances as wellesthe resistences of theY differential circuit. Y

Having thus described our invention and illustrated its use, .what we clztirn asunew and desire to secure by Letters Patent is the following: 4

1. The combination in a lmeansor locating ore bodies of en -audio'frequency 4generator, an exploring coil connectedlimel belmeeste :moed circuit therewith, and means cornprising an audio frequency am lier for indicating-any1 disturbance the'` elsmce of said circuit.

2. In a means for locatingbddies of ore 'and determining the magnitude thereof. said means comprising l a vacuumftubewamliier, an exploring coil excited by an audio requeney generator connected :1n a normally balanced` circuit therewith and an adgustablevmeans'in said circuit or malinta/igmthe balance thereof. t

e method -of locatin ore bodies which consists in .subjecting t Ye'ore bodies 35 to en; audio frequency alternatin current magnetic fieldaind measuring the a sorption of energy by the eddy currentsinduced. in

said ore' bodies.

,WENDELLL oA'RLsoN. sinne. rtANsoN. 

